Early Monday afternoon Harvey forecast update

Monday, 2:15pm CT— Good afternoon. After our break last night, rains have returned to the picture this morning and afternoon. Any rain adds insult to injury right now, but at least the rainfall rates have been, for the most part, under 1.50 inches per hour. This is small comfort obviously, but versus the rates we saw on Saturday night and Sunday, the word “manageable” keeps coming up. As manageable as something can be in this situation.

Now

As of 2 PM, radar is active, with steady moderate to locally heavy rainfall across the southern half of the Houston metro area.

Weather radar as of 2 PM is not optimal. (GR Level 3)

North of I-10 is seeing steady light to moderate rain persist as well. Rainfall rates as of 2 PM are about 0.25″ to 0.50″ per hour north of I-10 and 0.50″ to 1.50″ south of I-10. Again, insulting, infuriating, frustrating, but mostly manageable. It just really slows down drainage. Steady northeast winds inland and southeast winds at the coast are not helping matters either. There have been gusts to 40 or 45 mph, and that looks to continue, although significant increases beyond this are unlikely.

Rest of Today

What you see is what you get. Expect this rain to stay in place much of the afternoon. Rain may fall heavily at times, especially south of I-10. Winds will stay occasionally gusty. Wish we had better news on this front, but it’s going to be a pretty miserable Monday, and hopefully the rates stay at this manageable level. We feel they ought to.

Tonight and Tuesday

I don’t expect a lot of change tonight. Rain will likely fall steadily through the night, and into Tuesday morning. Harvey’s general east or southeast movement will pretty much lock things in. As Harvey begins to shift northward on Tuesday, we will start to see the rain become a little more sporadic I think. Steady moderate rain much of the time Tuesday morning into the afternoon. Harvey should make another landfall Wednesday near High Island, TX as a weak to moderate tropical storm (no significant strengthening is likely).

Official NHC forecast is not changed much, with our horrible storm finally exiting on Wednesday. (NHC)

This remains first and foremost a rain issue, and you should continue to monitor the water. Steady rain should end Wednesday and daily storm chances trend to close to zero by Thursday. We should see sunshine and much better weather to end the week, and we can begin our road to recovery. Stay safe all.

Posted at 2:15 PM CT Monday by Matt

Harvey almost certainly the biggest US flood-producing storm

Monday, 1pm CT—Houston remains in the midst of Hurricane Harvey’s devastating aftermath, and we are weeks if not months away from a full accounting of its toll on the fourth largest city in the United States. And while a definitive account of its epic proportions will have to wait, we can at least begin to make some preliminary assessments.

In this post we will discuss how Harvey compares to other major flood storms in US history, and also how it stacks up to the region’s previous flooding event of record, Tropical Storm Allison. (Spoiler alert: Allison had a good run, but Harvey has forever dethroned her).

Mississippi discharges

The Texas state climatologist, John Nielsen-Gammon, has been closely tracking Harvey and its attendant flooding. To gauge the overall impact of a rain event, he uses a metric that defines a target zone of 20,000 square miles (about the size of West Virginia, or about 30 times the size of the city of Houston), and then measures the rainfall rate over a 120-hour period in comparison to the discharge rate of the Mississippi River. Here are the top 10 Gulf Coast flood events, as measured in “Mississippi River discharges” over that time:

  • 3.6 Hurricane Harvey 2017 (estimate)
  • 3.4 Hurricane Beulah, 1967
  • 3.1 Brazos River flooding, 1899
  • 2.8 Hurricane Georges, 1998
  • 2.6 Southeast Texas flooding, 1994
  • 2.5 Louisiana floods, June 1940
  • 2.4 Tropical Storm Alberto, 1994
  • 2.3 November Texas floods, 1940
  • 2.3 Louisiana floods, 1953
  • 2.3 Tropical Storm Allison, 2001

Note that the initial estimate for Harvey may be too low. As of Monday morning, Neilsen-Gammon’s hand estimate for Harvey to date was 3.1, but more heavy rains were falling in the target area and a full five days not reached. Already, for 72 hours, Nielsen-Gammon said Harvey is the greatest event over this shorter time scale.

Under this metric of rainfall over a large area, then, Harvey will very likely produce the greatest total amount of rainfall in the United States from any single storm, at least during the last 120 years. (the Gulf coast is by far the most susceptible US regions to such events due to its proximity to the warm, humid body of tropical water).

See full post

Harvey late Monday morning: Rains remain, but storm finally moving

Monday, 10:30am CT—There is no way to escape the reality of the situation on the ground this morning: Houston bayous are flooding, and even after the region has received 30 inches of rain during the last two days, more is now falling over the central Houston area. It is a catastrophic situation. Finally, however, the end is in sight. Another day or two of this …

Harvey

Harvey remains barely a tropical storm, but its center moved into the Gulf of Mexico near Matagorda Bay this morning. Presently moving to the southeast at about 5 mph, some slight strengthening is possible over the next day or two as Harvey turns east, then northeast, but as discussed yesterday we are not too concerned about this possibility due to the lack of an organized core, and additionally some drier air is working into the storm. (See official track forecast).

Tropical Storm Harvey at 10am CT on Monday. (NOAA)

Overall, Harvey’s movement into the Gulf may be a positive development, because the storm is getting closer to being picked up by lower pressure in the Midwestern United States, which should lift it north. By later Tuesday, or Wednesday, we should hopefully be on the back side of the storm, with northerly winds helping to push water from inland bayous out to the Gulf of Mexico. Heavy rains should end, hopefully, by Wednesday or Wednesday night.

See full post

Early Monday morning Harvey Forecast Update

Good morning. Since about midnight, while it has continued to rain, totals have been held down a bit. Most of Harris County has seen less than an inch in that time, while a few spots west of Harris County and to the northeast, especially into Chambers and Liberty Counties have seen 1-3″ of rain. No rain helps, but these sorts of rains don’t hurt quite as badly.

Now

Radar this morning is opening up on a mostly positive note for us. Yes, again, more rain in the area, but a better view than 24 hours ago, and much better than some forecast models had indicated even 8-12 hours ago.

Radar as of 6 AM shows the heaviest rains oriented from about Beaumont and Lake Charles northwest to Livingston and Madisonville. (GR Level 3).

Scattered showers persist west of Houston and in other parts of the area.

Monday

Harvey has re-emerged in the Gulf near Matagorda. We, along with the National Hurricane Center, continue to believe that while Harvey will travel over the Gulf the next couple days, only modest re-organization is expected. Eric covered this in detail last night, and I see no reason things have changed much overnight. We don’t want you worrying about that, and everyone’s focus should continue to be on the rainfall forecast and ongoing flooding.

So what about rain today. Radar isn’t too alarming this morning, but we do expect rains to fill back in a bit as the day progresses. This is certainly not what folks want to hear, but I do believe that in most cases, the rainfall *rates* will be manageable enough to limit substantial new problems from occurring. What this will likely do is lead to some rises again on area bayous that have crested and are dropping now. Those that haven’t crested will continue to rise, albeit hopefully at a slower pace, despite new rains.

Tonight & Tuesday

As we go into tonight and tomorrow, expect continued periods of rain. Most of the time, rates should continue to be manageable so that things don’t worsen, but I can’t entirely rule out some heavier rainfall at times until Harvey comes ashore in Louisiana again on Tuesday night or Wednesday morning.

We figured this would be at least a four or five-day event for Houston, with the worst rains front-loaded in the first two or three days. Today begins day three, so we’re past the halfway point, and hopefully past most of the worst of the rains. That’s not to say we don’t have additional problems ahead, but our hope is that we can manage what is to come. We’ll have more for you a bit later this morning.

Posted at 6:20 AM Monday by Matt